Notes
Tides are the rise and fall of sea level caused mainly by the Moon's gravity (and the Sun's).
- Most coasts have two high tides and two low tides each lunar day (about 24 h 50 min).
- Spring tides have the greatest range and occur at new and full moon, when Sun, Earth and Moon line up.
- Neap tides have the smallest range and occur at the first and third quarter moons, when the Sun and Moon are at right angles.
- Tidal range is the difference between high and low tide: high 3.2 m, low 0.5 m gives 2.7 m.
Practice
Spring tides occur during:
Sun and Moon pull in a line.
A high tide of 4.1 m and a low tide of 0.9 m give a tidal range of:
$4.1 - 0.9 = 3.2$ m.
The main cause of tides is the:
Gravity from the Moon is the largest effect.
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